IADR Abstract Archives
Crosslink Density of Resin-based Composites Indirectly Measured With Soxhlet Extraction
Objectives: With regard to the leaching of components from composites, not only the degree of conversion, but also the crosslink density (CLD) of composites should be taken into account. CLD is important for the swelling behavior of composites, and subsequently also for the release of not cross-linked polymers/oligomers. So far, neither the CLD of composites nor the release of oligomers/polymers has been investigated.
Methods: Samples of composites (Z100, 3M ESPE; ELS and Microhybrid, Saremco) were prepared in a metal mold and light-cured as per instructions of the manufacturer (output=1100mW/cm2). Next the samples (n≥9) were subjected to soxhlet extraction for 24h in three different solvents (ethanol, toluene and water; at 120°C, 150°C and 130°C, respectively), and CLD was determined gravimetrically in terms of initial weight increase (swelling) and subsequent weight loss. To evaluate the release of oligomers/polymers, soxhlet extracts in tetrahydrofurane (n=3) were analyzed by gel permeation chromatography (GPC) (Shimadzu 10A, Shimadzu Scientific Instruments) and characterized by refractive index (RID-10A, Shimadzu) and ultra-violet absorption (SPD-10Avp, Shimadzu). Poly-HEMA (containing 2wt% camphorquinone and 2wt% ethyl-4-(dimethylamino)benzoate) and monomers (BisGMA, BisEMA, and TEGDMA) were used as controls. Additionally, the 24h-release of monomers in ethanol was measured with UPLC-MS/MS (Acquity Systems, Waters) after sample incubation (n=5).
Results: Most swelling (0.73wt%) and weight loss (-1.32wt%) was observed after soxhlet extraction in toluene. This signifies that the methyacrylate polymers in composites are highly cross-linked and do not dissolve well. The composite with the greatest swelling/weight loss, also released the highest amount of monomers (199.99±23.24nmol/mm2). GPC did not reveal significant release of oligomers.
Conclusions: CLD, measured indirectly with soxhlet extraction, is an important parameter regarding the leaching of components that should be taken into account in future studies. No oligomers were detected.
Methods: Samples of composites (Z100, 3M ESPE; ELS and Microhybrid, Saremco) were prepared in a metal mold and light-cured as per instructions of the manufacturer (output=1100mW/cm2). Next the samples (n≥9) were subjected to soxhlet extraction for 24h in three different solvents (ethanol, toluene and water; at 120°C, 150°C and 130°C, respectively), and CLD was determined gravimetrically in terms of initial weight increase (swelling) and subsequent weight loss. To evaluate the release of oligomers/polymers, soxhlet extracts in tetrahydrofurane (n=3) were analyzed by gel permeation chromatography (GPC) (Shimadzu 10A, Shimadzu Scientific Instruments) and characterized by refractive index (RID-10A, Shimadzu) and ultra-violet absorption (SPD-10Avp, Shimadzu). Poly-HEMA (containing 2wt% camphorquinone and 2wt% ethyl-4-(dimethylamino)benzoate) and monomers (BisGMA, BisEMA, and TEGDMA) were used as controls. Additionally, the 24h-release of monomers in ethanol was measured with UPLC-MS/MS (Acquity Systems, Waters) after sample incubation (n=5).
Results: Most swelling (0.73wt%) and weight loss (-1.32wt%) was observed after soxhlet extraction in toluene. This signifies that the methyacrylate polymers in composites are highly cross-linked and do not dissolve well. The composite with the greatest swelling/weight loss, also released the highest amount of monomers (199.99±23.24nmol/mm2). GPC did not reveal significant release of oligomers.
Conclusions: CLD, measured indirectly with soxhlet extraction, is an important parameter regarding the leaching of components that should be taken into account in future studies. No oligomers were detected.